Acidosis exacerbates in vivo IL-1-dependent inflammatory responses and neutrophil recruitment during pulmonary Pseudomonas aeruginosa infection

Unveiling cytokine charge disparity as a potential mechanism for immune regulation

Cytokines are small signaling proteins that regulate the immune responses to infection and tissue damage. Surface charges of cytokines determine their in vivo fate in immune regulation, e.g., half-life and distribution. The overall negative charges in the extracellular microenvironment and the acidosis during inflammation and infection may differentially impact cytokines with different surface charges for fine-tuned immune regulation via controlling tissue residential properties. However, the trend and role of cytokine surface charges has yet to be elucidated in the literature. Interestingly, we have observed that most pro-inflammatory cytokines have a negative charge, while most anti-inflammatory cytokines and chemokines have a positive charge. In this review, we extensively examined the surface charges of all cytokines and chemokines, summarized the pharmacokinetics and tissue adhesion of major cytokines, and analyzed the link of surface charge with cytokine biodistribution, activation, and function in immune regulation. Additionally, we identified that the general trend of charge disparity between pro- and anti-inflammatory cytokines represents a unique opportunity to develop precise immune modulation approaches, which can be applied to many inflammation-associated diseases including solid tumors, chronic wounds, infection, and sepsis.

Inflammatory liver diseases and susceptibility to sepsis

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

NETosis is critical in patients with severe community-acquired pneumonia

Pneumonia is the fourth leading cause of death globally, and the reason for the high mortality rate of patients with severe community-acquired pneumonia (SCAP) remains elusive. Corticosteroid treatment reduces mortality in adults with SCAP but can cause numerous adverse events. Therefore, novel therapeutic targets need to be explored and new adjunctive immune drugs are urgently required. We analyzed the transcriptome data of peripheral blood leukocytes from patients with SCAP and healthy controls from three perspectives: differentially expressed genes, predicted functions of differentially expressed long non-coding RNAs, and transcriptional read-through. We discovered that the NETosis pathway was top-ranked in patients with SCAP caused by diverse kinds of pathogens. This provides a potential therapeutic strategy for treating patients. Furthermore, we calculated the correlation between the expression of genes involved in NETosis and the ratio of arterial oxygen partial pressure to fractional inspired oxygen. We identified four novel potential therapeutic targets for NETosis in patients with SCAP, including H4C15, H3-5, DNASE1, and PRKCB. In addition, a higher occurrence of transcriptional read-through is associated with a worse outcome in patients with SCAP, which probably can explain the high mortality rate of patients with SCAP.

Understanding lactate sensing and signalling

Metabolites generated from cellular and tissue metabolism have been rediscovered in recent years as signalling molecules. They may act as cofactor of enzymes or be linked to proteins as post-translational modifiers. They also act as ligands for specific receptors, highlighting that their neglected functions have, in fact, a long standing in evolution. Lactate is one such metabolite that has been considered for long time a waste product of metabolism devoid of any biological function. However, in the past 10 years, lactate has gained much attention in several physio-pathological processes. Mechanisms of sensing and signalling have been discovered and implicated in a broad range of diseases, from cancer to inflammation and fibrosis, providing opportunities for novel therapeutic avenues. Here, we review some of the most recently discovered mechanisms of lactate sensing and signalling.

Airway acidification impaired host defense against Pseudomonas aeruginosa infection by promoting type 1 interferon β response

Airway microenvironment played an important role in the progression of chronic respiratory disease. Here we showed that standardized pondus hydrogenii (pH) of exhaled breath condensate (EBC) of bronchiectasis patients was significantly lower than that of controls and was significantly correlated with bronchiectasis severity index (BSI) scores and disease prognosis. EBC pH was lower in severe patients than that in mild and moderate patients. Besides, acidic microenvironment deteriorated Pseudomonas aeruginosa (P. aeruginosa) pulmonary infection in mice models. Mechanistically, acidic microenvironment increased P. aeruginosa outer membrane vesicles (PA_OMVs) released and boosted it induced the activation of interferon regulatory factor3 (IRF3)-interferonβ (IFN-β) signalling pathway, ultimately compromised the anti-bacteria immunity. Targeted knockout of IRF3 or type 1 interferon receptor (IFNAR1) alleviated lung damage and lethality of mice after P. aeruginosa infection that aggravated by acidic microenvironment. Together, these findings identified airway acidification impaired host resistance to P. aeruginosa infection by enhancing it induced the activation of IRF3-IFN-β signalling pathway. Standardized EBC pH may be a useful biomarker of disease severity and a potential therapeutic target for the refractory P. aeruginosa infection. The study also provided one more reference parameter for drug selection and new drug discovery for bronchiectasis.

Trehalose coated nanocellulose to inhibit the infections by S. aureus

Preventing bacterial infection by using antiadhesive compounds is one alternative to antibiotic treatment. Trehalose based polymers can serve as an antiadhesive agent that are selective to bacteria as trehalose is...

Engineered mesenchymal stromal cell therapy during human lung ex vivo lung perfusion is compromised by acidic lung microenvironment

Ex vivo lung perfusion (EVLP) is an excellent platform to apply novel therapeutics, such as gene and cell therapies, before lung transplantation. We investigated the concept of human donor lung engineering during EVLP by combining gene and cell therapies. Premodified cryopreserved mesenchymal stromal cells with augmented anti-inflammatory interleukin-10 production (MSCIL-10) were administered during EVLP to human lungs that had various degrees of underlying lung injury. Cryopreserved MSCIL-10 had excellent viability, and they immediately and efficiently elevated perfusate and lung tissue IL-10 levels during EVLP. However, MSCIL-10 function was compromised by the poor metabolic conditions present in the most damaged lungs. Similarly, exposing cultured MSCIL-10 to poor metabolic, and especially acidic, conditions decreased their IL-10 production. In conclusion, we found that "off-the-shelf" MSCIL-10 therapy of human lungs during EVLP is safe and feasible, and results in rapid IL-10 elevation, and that the acidic target-tissue microenvironment may compromise the efficacy of cell-based therapies.

Impact of Lipid/Magnesium Hydroxide Hybrid Nanoparticles on the Stability of Vascular Endothelial Growth Factor-Loaded PLGA Microspheres

The purpose of the present study is to characterize poly(d,l-lactide-co-glycolide) (PLGA) composite microcarriers for vascular endothelial growth factor (VEGF) delivery. To reduce the initial burst release and protect the bioactivity, VEGF is encapsulated in soybean l-α-phosphatidylethanolamine (PE) and l-α-phosphatidylcholine (PC) anhydrous reverse micelle (VEGF-RM) nanoparticles. Also, mesoporous nano-hexagonal Mg(OH)₂ nanostructure (MNS)-loaded PE/PC anhydrous reverse micelle (MNS-RM) nanoparticles are synthesized to suppress the induced inflammation of PLGA acidic byproducts and regulate the release profile. The flow-focusing microfluidic geometry platforms are used to fabricate different combinations of PLGA composite microspheres (PLGA-CMPs) with MNSs, MNS-RM, VEGF-RM, and native VEGF. The essential parameters of each formulation, such as release profiles, encapsulation efficacy, bioactivity, inflammatory response, and cytotoxicity, are investigated by in vitro and in vivo studies. The results indicate that generated acidic byproducts during the hydrolytic degradation process of PLGA can be buffered, and pH values inside and outside microspheres can remain steady during degradation by MNSs. Furthermore, the significant improvement in the stability of the encapsulated VEGF is confirmed by the bioactivity assay. In vitro release study shows that the VEGF initial burst release is well minimized in the present microcarriers. The present monodisperse PLGA-CMPs can be widely used in various tissue engineering and therapeutic applications.

Radiotherapy programs neutrophils to an antitumor phenotype by inducing mesenchymal-epithelial transition

Background

Neutrophils can play a pro-tumor or anti-tumor role depending on the tumor microenvironment. The effects of concurrent treatment with granulocyte colony-stimulating factor (G-CSF) and radiotherapy (RT) on neutrophils have not yet to be described.

Methods

Hypofractionated radiation of 8 Gy ×3 fractions was administered with or without recombinant G-CSF to Lewis lung carcinoma tumor-bearing C57BL/6 model mice. The activation status of cytotoxic T cells in the mice was measured, along with the levels of tumor-associated neutrophils, cytotoxic T cells, and Treg cells. Tumor growth, survival, cytokine expression, and signaling pathways underlying anti-tumor effects of tumor-associated neutrophils after treatment were also studied. To ascertain the effects of concurrent RT and G-CSF on tumor-associated neutrophils, neutrophil depletion was performed.

Results

RT affected early neutrophil infiltration, which is the first-line immune response. Subsequently, enhanced accumulation of lymphocytes, particularly CD8 cytotoxic T cells, was observed. Notably, lymphocytic infiltration was inhibited by neutrophil depletion but enhanced by G-CSF treatment. RT generated persistent DNA damage, as evidenced by an accumulation of phosphorylation of histone H2AX (γH2AX), and subsequently triggered inflammatory chemokine secretion. The chemokines CXCL1, CXCL2, and CCL5 were upregulated in both radiation-treated cells and the corresponding supernatants. Neutrophils that were newly recruited after RT improved radiosensitivity by inhibiting epithelial-mesenchymal transition via the reactive oxygen species-mediated PI3K/Akt/Snail signaling pathway, and G-CSF treatment enhanced this effect.

Conclusions

The results of this study suggest that RT activates neutrophil recruitment and polarizes newly recruited neutrophils toward an antitumor phenotype, which is enhanced by the concurrent administration of G-CSF. Mesenchymal-epithelial transition induced by reactive oxygen species accumulation plays a major role in this process. Thus, the polarization of tumor-associated neutrophils might play a role in future cancer immunotherapies.

The Role of Innate Immunity in Pulmonary Infections

Innate immunity forms a protective line of defense in the early stages of pulmonary infection. The primary cellular players of the innate immunity against respiratory infections are alveolar macrophages (AMs), dendritic cells (DCs), neutrophils, natural killer (NK) cells, and innate lymphoid cells (ILCs). They recognize conserved structures of microorganisms through membrane-bound and intracellular receptors to initiate appropriate responses. In this review, we focus on the prominent roles of innate immune cells and summarize transmembrane and cytosolic pattern recognition receptor (PRR) signaling recognition mechanisms during pulmonary microbial infections. Understanding the mechanisms of PRR signal recognition during pulmonary pathogen infections will help us to understand pulmonary immunopathology and lay a foundation for the development of effective therapies to treat and/or prevent pulmonary infections.

Real-time measurement of cellular bioenergetics in fully differentiated human nasal epithelial cells grown at air-liquid-interface

Shifts in cellular metabolic phenotypes have the potential to cause disease-driving processes in respiratory disease. The respiratory epithelium is particularly susceptible to metabolic shifts in disease, but our understanding of these processes is limited by the incompatibility of the technology required to measure metabolism in real-time with the cell culture platforms used to generate differentiated respiratory epithelial cell types. Thus, to date, our understanding of respiratory epithelial metabolism has been restricted to that of basal epithelial cells in submerged culture, or via indirect end point metabolomics readouts in lung tissue. Here we present a novel methodology using the widely available Seahorse Analyzer platform to monitor real-time changes in the cellular metabolism of fully differentiated primary human airway epithelial cells grown at air-liquid interface (ALI). We show increased glycolytic, but not mitochondrial, ATP production rates in response to physiologically relevant increases in glucose availability. We also show that pharmacological inhibition of lactate dehydrogenase is able to reduce glucose-induced shifts toward aerobic glycolysis. This method is timely given the recent advances in our understanding of new respiratory epithelial subtypes that can only be observed in vitro through culture at ALI and will open new avenues to measure real-time metabolic changes in healthy and diseased respiratory epithelium, and in turn the potential for the development of novel therapeutics targeting metabolic-driven disease phenotypes.

Genetically engineered distal airway stem cell transplantation protects mice from pulmonary infection

Severe pulmonary infection is a major threat to human health accompanied by substantial medical costs, prolonged inpatient requirements, and high mortality rates. New antimicrobial therapeutic strategies are urgently required to address the emergence of antibiotic resistance and persistent bacterial infections. In this study, we show that the constitutive expression of a native antimicrobial peptide LL-37 in transgenic mice aids in clearing Pseudomonas aeruginosa (PAO1), a major pathogen of clinical pulmonary infection. Orthotopic transplantation of adult mouse distal airway stem cells (DASCs), genetically engineered to express LL-37, into injured mouse lung foci enabled large-scale incorporation of cells and long-term release of the host defense peptide, protecting the mice from bacterial pneumonia and hypoxemia. Further, correlates of DASCs in adult humans were isolated, expanded, and genetically engineered to demonstrate successful construction of an anti-infective artificial lung. Together, our stem cell-based gene delivery therapeutic platform proposes a new strategy for addressing recurrent pulmonary infections with future translational opportunities.

Influence of pH on the activity of finafloxacin against extracellular and intracellular Burkholderia thailandensis, Yersinia pseudotuberculosis and Francisella philomiragia and on its cellular pharmacokinetics in THP-1 monocytes

OBJECTIVES

Burkholderia pseudomallei, Yersinia pestis and Francisella tularensis are facultative intracellular bacteria causing life-threatening infections. We have (a) compared the activity of finafloxacin (a fluoroquinolone in development showing improved activity at acidic pH) with that of ciprofloxacin, levofloxacin and imipenem against the extracellular and intracellular (THP-1 monocytes) forms of infection by attenuated surrogates of these species (B. thailandensis, Y. pseudotuberculosis, F. philomiragia) and (b) assessed finafloxacin cellular pharmacokinetics (accumulation, distribution, efflux).

METHODS

Bacteria in broth or in infected monocytes were exposed to antibiotics at pH 7.4 or 5.5 for 24 hr. Maximal relative efficacies (E_max) and static concentrations (C_s) were calculated using the Hill equation (concentration-response curves). Finafloxacin pharmacokinetics in cells at pH 7.4 or 5.5 was investigated using ¹⁴C-labelled drug.

RESULTS

Extracellularly, all drugs sterilized the cultures, with finafloxacin being two to six times more potent at acidic pH. Intracellularly, E_max reached the limit of detection (4-5 log₁₀ cfu decrease) for finafloxacin against all species, but only against B. thailandensis and F. philomiragia for ciprofloxacin and levofloxacin, while imipenem caused less than 2 log₁₀ cfu decrease for all species. At acid pH, C_s shifted to two to five times lower values for finafloxacin and to one to four times higher values for the other drugs. Finafloxacin accumulated in THP-1 cells by approximately fivefold at pH 7.4 but up to 20-fold at pH 5.5, and distributed in the cytosol.

CONCLUSIONS

Fluoroquinolones have proven to be effective in reducing the intracellular reservoirs of B. thailandensis, Y. pseudotuberculosis and F. philomiragia, with finafloxacin demonstrating an additional advantage in acidic environments.

Real-Time, Semi-Automated Fluorescent Measurement of the Airway Surface Liquid pH of Primary Human Airway Epithelial Cells

In recent years, the importance of mucosal surface pH in the airways has been highlighted by its ability to regulate airway surface liquid (ASL) hydration, mucus viscosity and activity of antimicrobial peptides, key parameters involved in innate defense of the lungs. This is of primary relevance in the field of chronic respiratory diseases such as cystic fibrosis (CF) where these parameters are dysregulated. While different groups have studied ASL pH both in vivo and in vitro, their methods report a relatively wide range of ASL pH values and even contradictory findings regarding any pH differences between non-CF and CF cells. Furthermore, their protocols do not always provide enough details in order to ensure reproducibility, most are low throughput and require expensive equipment or specialized knowledge to implement, making them difficult to establish in most labs. Here we describe a semi-automated fluorescent plate reader assay that enables the real-time measurement of ASL pH under thin film conditions that more closely resemble the in vivo situation. This technique allows for stable measurements for many hours from multiple airway cultures simultaneously and, importantly, dynamic changes in ASL pH in response to agonists and inhibitors can be monitored. To achieve this, the ASL of fully differentiated primary human airway epithelial cells (hAECs) are stained overnight with a pH-sensitive dye in order to allow for the reabsorption of the excess fluid to ensure thin film conditions. After fluorescence is monitored in the presence or absence of agonists, pH calibration is performed in situ to correct for volume and dye concentration. The method described provides the required controls to make stable and reproducible ASL pH measurements, which ultimately could be used as a drug discovery platform for personalized medicine, as well as adapted to other epithelial tissues and experimental conditions, such as inflammatory and/or host-pathogen models.

Unravelling the Interplay between Extracellular Acidosis and Immune Cells

The development of an acidic tissue environment is a hallmark of a variety of inflammatory processes and solid tumors. However, little attention has been paid so far to analyze the influence exerted by extracellular pH on the immune response. Tissue acidosis (pH 6.0 to 7.0) is usually associated with the course of infectious processes in peripheral tissues. Moreover, it represents a prominent feature of solid tumors. In fact, values of pH ranging from 5.7 to 7.0 are usually found in a number of solid tumors such as breast cancer, brain tumors, sarcomas, malignant melanoma, squamous cell carcinomas, and adenocarcinomas. Both the innate and adaptive arms of the immune response appear to be finely regulated by extracellular acidosis in the range of pH values found at inflammatory sites and tumors. Low pH has been shown to delay neutrophil apoptosis, promoting their differentiation into a proangiogenic profile. Acting on monocytes and macrophages, it induces the activation of the inflammasome and the production of IL-1β, while the exposure of conventional dendritic cells to low pH promotes the acquisition of a mature phenotype. Overall, these observations suggest that high concentrations of protons could be recognized by innate immune cells as a danger-associated molecular pattern (DAMP). On the other hand, by acting on T lymphocytes, low pH has been shown to suppress the cytotoxic response mediated by CD8+ T cells as well as the production of IFN-γ by TH1 cells. Interestingly, modulation of tumor microenvironment acidity has been shown to be able not only to reverse anergy in human and mouse tumor-infiltrating T lymphocytes but also to improve the antitumor immune response induced by checkpoint inhibitors. Here, we provide an integrated view of the influence exerted by low pH on immune cells and discuss its implications in the immune response against infectious agents and tumor cells.

Fisetin inhibits the generation of inflammatory mediators in interleukin-1β-induced human lung epithelial cells by suppressing the NF-κB and ERK1/2 pathways

Fisetin, a flavone that can be isolated from fruits and vegetables, has anti-tumor and anti-oxidative properties and ameliorates airway hyperresponsiveness in asthmatic mice. This study investigated whether fisetin can suppress the expression of inflammatory mediators and intercellular adhesion molecule 1 (ICAM-1) in A549 human lung epithelial cells that were stimulated with interleukin-1β (IL-1β) to induce inflammatory responses. A549 cells were treated with fisetin (3-30 μM) and then with IL-1β. Fisetin significantly inhibited COX-2 expression and reduced prostaglandin E₂ production, and it suppressed the levels of IL-8, CCL5, monocyte chemotactic protein 1, tumor necrosis factor α, and IL-6. Fisetin also significantly attenuated the expression of chemokine and inflammatory cytokine genes and decreased the expression of ICAM-1, which mediates THP-1 monocyte adhesion to inflammatory A549 cells. Fisetin decreased the translocation of nuclear transcription factor kappa-B (NF-κB) subunit p65 into the nucleus and inhibited the phosphorylation of proteins in the ERK1/2 pathway. Co-treatment of IL-1β-stimulated A549 cells with ERK1/2 inhibitors plus fisetin reduced ICAM-1 expression. Furthermore, fisetin significantly increased the effects of the protective antioxidant pathway by promoting the expression of nuclear factor erythroid-2-related factor-2 and heme oxygenase 1. Taken together, these data suggest that fisetin has anti-inflammatory effects and that it suppresses the expression of chemokines, inflammatory cytokines, and ICAM-1 by suppressing the NF-κB and ERK1/2 signaling pathways in IL-1β-stimulated human lung epithelial A549 cells.

Carbonic anhydrase IX is a critical determinant of pulmonary microvascular endothelial cell pH regulation and angiogenesis during acidosis

Carbonic anhydrase IX (CA IX) is highly expressed in rapidly proliferating and highly glycolytic cells, where it serves to enhance acid-regulatory capacity. Pulmonary microvascular endothelial cells (PMVECs) actively utilize aerobic glycolysis and acidify media, whereas pulmonary arterial endothelial cells (PAECs) primarily rely on oxidative phosphorylation and minimally change media pH. Therefore, we hypothesized that CA IX is critical to PMVEC angiogenesis because of its important role in regulating pH. To test this hypothesis, PMVECs and PAECs were isolated from Sprague-Dawley rats. CA IX knockout PMVECs were generated using the CRISPR-Cas9 technique. During serum-stimulated growth, mild acidosis (pH 6.8) did not affect cell counts of PMVECs, but it decreased PAEC cell number. Severe acidosis (pH 6.2) decreased cell counts of PMVECs and elicited an even more pronounced reduction of PAECs. PMVECs had a higher CA IX expression compared with PAECs. CA activity was higher in PMVECs compared with PAECs, and enzyme activity was dependent on the type IX isoform. Pharmacological inhibition and genetic ablation of CA IX caused profound dysregulation of extra- and intracellular pH in PMVECs. Matrigel assays revealed impaired angiogenesis of CA IX knockout PMVECs in acidosis. Lastly, pharmacological CA IX inhibition caused profound cell death in PMVECs, whereas genetic CA IX ablation had little effect on PMVEC cell death in acidosis. Thus CA IX controls PMVEC pH necessary for angiogenesis during acidosis. CA IX may contribute to lung vascular repair during acute lung injury that is accompanied by acidosis within the microenvironment.